Chapter 1 - The Study of
Body Function
• Physiology – Study of biological function.
– Our emphasis is on cellular mechanisms, i.e. how
the structure accomplishes its tasks.
• [read about the development of pharmaceutical drugs]..
Homeostasis
• All the regulatory mechanisms of the body
work in concert to maintain a constant
internal environment despite changes in the
external environment.
• Our focus will be how body organs contribute
to homeostasis.
• We define and “gauge sickness” in terms of
deviations from the norm. If your internal
environment can not be maintained at the
constant level, you are sick..
• Homeostasis is most commonly regulated by
Negative feedback.
• Negative feedback occurs when sensors are
activated by changes in the internal
environment, i.e. deviations from the set
point.
• The sensors activate effectors (smooth
muscle, cardiac muscle, or glands), which
increase or decrease their activities.
• The altered functions of the effectors produce
a change in the opposite direction from the
sensor until the set point is again reached..
Negative Feedback
Negative Feedback
Homeostatic mechanism regulates body temperature
Control center
Slide number: 1
The brain detects the
deviation from the set
point and signals effector
organs.
Receptors
Effectors
Skin blood vessels dilate
and sweat glands secrete.
Thermoreceptors send
signals to the control center.
Stimulus
Response
Body temperature
rises above normal.
Body heat is lost to surroundings,
temperature drops toward normal.
too high
Normal body
Temperature
37oC (98.6oF)
too low
Stimulus
Response
Body temperature
drops below normal.
Body heat is conserved,
temperature rises toward normal.
Receptors
Effectors
Effectors
Thermoreceptors send
signals to the control center.
Skin blood vessels constrict and
sweat glands remain inactive.
generates body heat.
Control center
The brain detects the
deviation from the set point
and signals effector organs.
If body temperature
continues to drop, control
center signals muscles to
contract involuntarily.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 2
Stimulus
Body temperature
rises above normal.
too high
Normal body
Temperature
37oC (98.6oF)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 3
Receptors
Thermoreceptors send
signals to the control center.
Stimulus
Body temperature
rises above normal.
too high
Normal body
Temperature
37oC (98.6oF)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 4
Control center
The brain detects the
deviation from the set
point and signals effector
organs.
Receptors
Thermoreceptors send
signals to the control center.
Stimulus
Body temperature
rises above normal.
too high
Normal body
Temperature
37oC (98.6oF)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 5
Control center
The brain detects the
deviation from the set
point and signals effector
organs.
Receptors
Effectors
Thermoreceptors send
signals to the control center.
Skin blood vessels dilate
and sweat glands secrete.
Stimulus
Body temperature
rises above normal.
too high
Normal body
Temperature
37oC (98.6oF)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 6
Control center
The brain detects the
deviation from the set
point and signals effector
organs.
Receptors
Effectors
Thermoreceptors send
signals to the control center.
Skin blood vessels dilate
and sweat glands secrete.
Stimulus
Response
Body temperature
rises above normal.
Body heat is lost to surroundings,
temperature drops toward normal.
too high
Normal body
Temperature
37oC (98.6oF)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 7
Normal body
Temperature
37oC (98.6oF)
too low
Stimulus
Body temperature
drops below normal.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 8
Normal body
Temperature
37oC (98.6oF)
too low
Stimulus
Body temperature
drops below normal.
Receptors
Thermoreceptors send
signals to the control center.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 9
Normal body
Temperature
37oC (98.6oF)
too low
Stimulus
Body temperature
drops below normal.
Receptors
Thermoreceptors send
signals to the control center.
Control center
The brain detects the
deviation from the set point
and signals effector organs.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 10
Normal body
Temperature
37oC (98.6oF)
too low
Stimulus
Body temperature
drops below normal.
Receptors
Thermoreceptors send
signals to the control center.
Control center
The brain detects the
deviation from the set point
If body temperature
and signals effector organs.
continues to drop, control
center signals muscles to
contract involuntarily.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 11
Normal body
Temperature
37oC (98.6oF)
too low
Stimulus
Body temperature
drops below normal.
Receptors
Effectors
Effectors
Thermoreceptors send
Skin blood vessels constrict and Muscle activity
signals to the control center. sweat glands remain inactive.
generates body heat.
Control center
The brain detects the
deviation from the set point
If body temperature
and signals effector organs.
continues to drop, control
center signals muscles to
contract involuntarily.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Homeostatic mechanism regulates body temperature
Slide number: 12
Normal body
Temperature
37oC (98.6oF)
too low
Stimulus
Response
Body temperature
drops below normal.
Body heat is conserved,
temperature rises toward normal.
Receptors
Effectors
Effectors
Thermoreceptors send
Skin blood vessels constrict and Muscle activity
signals to the control center. sweat glands remain inactive.
generates body heat.
Control center
The brain detects the
deviation from the set point
If body temperature
and signals effector organs.
continues to drop, control
center signals muscles to
contract involuntarily.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Positive feedback also occurs, although less
commonly.
• Positive feedback occurs when the action of
the effector amplifies those changes that
stimulated the sensors..
• Homeostasis is regulated by two general
categories of regulatory mechanisms:
– Intrinsic: “built-in” to organs under
regulation.
• e.g. the presence or absence of gap junctions
in heart muscle regulates the speed of each
cardiac cycle.
– Extrinsic: outside the organ.
• e.g. regulation by the nervous and/or endocrine
systems..
Review Primary Tissues